Impact printers, such as for example, dot matrix printers, have conventionally employed inking means in the form of a ribbon saturated with ink and positioned between the print receiving medium and the printing tips of the reciprocating print wires which drive the ribbon against the print receiving medium, causing ink in the region of the ribbon impacted by the print wire tip to be transferred to the print receiving medium, the shape of the area formed on the print receiving medium by the transferred ink substantially conforming to the cross-sectional configuration of the print wire, which is typically circular, thereby forming a dot upon the print receiving medium.
The use of ink ribbons necessitates a mechanism for supporting the ribbon, driving the ribbon and both unreeling and taking up the ribbon. Ribbons are susceptible to breakage and are clumsy and messy to replace. The well-known ribbon systems employing take-up and supply reels have since been replaced to a large degree by cartridge assemblies which are simpler and not quite as messy to remove and replace. However, such cartridge assemblies are expensive and require rather frequent replacement.
The disadvantages of the conventional ink ribbon has led to the development of a direct delivery system described, for example, in copending application Ser. No. 901,182, filed Apr. 28, 1978, now U.S. Pat. No. 4,194,846 issued Mar. 25, 1980, and assigned to the assignee of the present applicaton. The system described therein teaches an ink container for delivering liquid printing material to the sides of the print wires. The ink along the sides is then conveyed to the tips of the print wires which transfer the liquid printing material to a print receiving medium when the tips are impacted against said medium. Although this design totally eliminates the need for an inked ribbon and all of its accompanying disadvantages, it has been found that the apparatus described in the aforementioned U.S. patent lacks means to accurately regulate the amount of ink delivered to the print wires, in that the system described therein has been found to drip and splatter ink, causing smudging of the ink resulting in a noticeable reduction in print quality. The ink has also been found to dry out prematurely. An effort to solve some of these problems has led to the development of the direct inking system described in U.S. application Ser. No. 044,758, filed in the U.S. Patent Office on June 1, 1979, filed by this inventor and assigned to the assignee of the present application. The system described therein teaches a capillary member mounted within the print head and cooperating with a capillary member mounted within the ink container for delivering ink to the print wires a spaced distance inwardly from the forward printing tips and further incorporating sponge-like absorbent elements positioned between the printing tips and the print head capillary members for controlling the flow of ink forwardly from the print head capillary members to the printing tips and further serving as an intermediary ink storage means.
One of the objectives that the present inventor has strived to attain is the design of a universal direct inking system for print heads which is capable of being used in printers having variable printing speed, as well as being capable of being used over a larger range of different printers, each having different printing speeds. For example, it is obvious that a dot matrix printer model capable of printing at twice the speed of another dot matrix printer model requires that ink be capable of being delivered to the printing tips at twice the rate. It has been found that the direct inking system described in the aforementioned U.S. patent, and in pending application Ser. No. 44,758, is incapable of providing an arrangement in which ink flow is capable of accommodating very high speed printers and which may be regulated to accommodate significant differences in printing speed. In addition to the above, it is important to be able to provide relatively fine adjustments in ink control to prevent ink splattering as a result of too great an ink flow rate which may result, for example, due to significant increases in ambient temperature conditions which affect ink viscosity, for example.